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<div class="titlepage"><div><div><h4 class="title">
<a name="boost_asio.reference.read_until.overload23"></a><a class="link" href="overload23.html" title="read_until (23 of 24 overloads)">read_until
        (23 of 24 overloads)</a>
</h4></div></div></div>
<p>
          Read data into a dynamic buffer sequence until a function object indicates
          a match.
        </p>
<pre class="programlisting">template&lt;
    typename <a class="link" href="../SyncReadStream.html" title="Buffer-oriented synchronous read stream requirements">SyncReadStream</a>,
    typename <a class="link" href="../DynamicBuffer_v2.html" title="Dynamic buffer requirements (version 2)">DynamicBuffer_v2</a>,
    typename MatchCondition&gt;
std::size_t read_until(
    SyncReadStream &amp; s,
    DynamicBuffer_v2 buffers,
    MatchCondition match_condition,
    typename constraint&lt; is_match_condition&lt; MatchCondition &gt;::value &gt;::type  = 0,
    typename constraint&lt; is_dynamic_buffer_v2&lt; DynamicBuffer_v2 &gt;::value &gt;::type  = 0);
</pre>
<p>
          This function is used to read data into the specified dynamic buffer sequence
          until a user-defined match condition function object, when applied to the
          data contained in the dynamic buffer sequence, indicates a successful match.
          The call will block until one of the following conditions is true:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              The match condition function object returns a std::pair where the second
              element evaluates to true.
            </li>
<li class="listitem">
              An error occurred.
            </li>
</ul></div>
<p>
          This operation is implemented in terms of zero or more calls to the stream's
          read_some function. If the match condition function object already indicates
          a match, the function returns immediately.
        </p>
<h6>
<a name="boost_asio.reference.read_until.overload23.h0"></a>
          <span class="phrase"><a name="boost_asio.reference.read_until.overload23.parameters"></a></span><a class="link" href="overload23.html#boost_asio.reference.read_until.overload23.parameters">Parameters</a>
        </h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl class="variablelist">
<dt><span class="term">s</span></dt>
<dd><p>
                The stream from which the data is to be read. The type must support
                the SyncReadStream concept.
              </p></dd>
<dt><span class="term">buffers</span></dt>
<dd><p>
                A dynamic buffer sequence into which the data will be read.
              </p></dd>
<dt><span class="term">match_condition</span></dt>
<dd>
<p>
                The function object to be called to determine whether a match exists.
                The signature of the function object must be:
</p>
<pre class="programlisting">pair&lt;iterator, bool&gt; match_condition(iterator begin, iterator end);
</pre>
<p>
                where <code class="computeroutput">iterator</code> represents the type:
</p>
<pre class="programlisting">buffers_iterator&lt;typename DynamicBuffer_v2::const_buffers_type&gt;
</pre>
<p>
                The iterator parameters <code class="computeroutput">begin</code> and <code class="computeroutput">end</code> define
                the range of bytes to be scanned to determine whether there is a
                match. The <code class="computeroutput">first</code> member of the return value is an iterator
                marking one-past-the-end of the bytes that have been consumed by
                the match function. This iterator is used to calculate the <code class="computeroutput">begin</code>
                parameter for any subsequent invocation of the match condition. The
                <code class="computeroutput">second</code> member of the return value is true if a match
                has been found, false otherwise.
              </p>
</dd>
</dl>
</div>
<h6>
<a name="boost_asio.reference.read_until.overload23.h1"></a>
          <span class="phrase"><a name="boost_asio.reference.read_until.overload23.return_value"></a></span><a class="link" href="overload23.html#boost_asio.reference.read_until.overload23.return_value">Return
          Value</a>
        </h6>
<p>
          The number of bytes in the dynamic_buffer's get area that have been fully
          consumed by the match function.
        </p>
<h6>
<a name="boost_asio.reference.read_until.overload23.h2"></a>
          <span class="phrase"><a name="boost_asio.reference.read_until.overload23.exceptions"></a></span><a class="link" href="overload23.html#boost_asio.reference.read_until.overload23.exceptions">Exceptions</a>
        </h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl class="variablelist">
<dt><span class="term">boost::system::system_error</span></dt>
<dd><p>
                Thrown on failure.
              </p></dd>
</dl>
</div>
<h6>
<a name="boost_asio.reference.read_until.overload23.h3"></a>
          <span class="phrase"><a name="boost_asio.reference.read_until.overload23.remarks"></a></span><a class="link" href="overload23.html#boost_asio.reference.read_until.overload23.remarks">Remarks</a>
        </h6>
<p>
          After a successful read_until operation, the dynamic buffer sequence may
          contain additional data beyond that which matched the function object.
          An application will typically leave that data in the dynamic buffer sequence
          for a subsequent read_until operation to examine.
        </p>
<p>
          The default implementation of the <code class="computeroutput">is_match_condition</code> type
          trait evaluates to true for function pointers and function objects with
          a <code class="computeroutput">result_type</code> typedef. It must be specialised for other user-defined
          function objects.
        </p>
<h6>
<a name="boost_asio.reference.read_until.overload23.h4"></a>
          <span class="phrase"><a name="boost_asio.reference.read_until.overload23.examples"></a></span><a class="link" href="overload23.html#boost_asio.reference.read_until.overload23.examples">Examples</a>
        </h6>
<p>
          To read data into a dynamic buffer sequence until whitespace is encountered:
        </p>
<pre class="programlisting">typedef boost::asio::buffers_iterator&lt;
    boost::asio::const_buffers_1&gt; iterator;

std::pair&lt;iterator, bool&gt;
match_whitespace(iterator begin, iterator end)
{
  iterator i = begin;
  while (i != end)
    if (std::isspace(*i++))
      return std::make_pair(i, true);
  return std::make_pair(i, false);
}
...
std::string data;
boost::asio::read_until(s, data, match_whitespace);
</pre>
<p>
          To read data into a <code class="computeroutput">std::string</code> until a matching character
          is found:
        </p>
<pre class="programlisting">class match_char
{
public:
  explicit match_char(char c) : c_(c) {}

  template &lt;typename Iterator&gt;
  std::pair&lt;Iterator, bool&gt; operator()(
      Iterator begin, Iterator end) const
  {
    Iterator i = begin;
    while (i != end)
      if (c_ == *i++)
        return std::make_pair(i, true);
    return std::make_pair(i, false);
  }

private:
  char c_;
};

namespace asio {
  template &lt;&gt; struct is_match_condition&lt;match_char&gt;
    : public boost::true_type {};
} // namespace asio
...
std::string data;
boost::asio::read_until(s, data, match_char('a'));
</pre>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2021 Christopher
      M. Kohlhoff<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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